Although devices providing six axis adjustment have uses in various scientific, technical and manufacturing applications, they are of particular interest to the electro-optics industry. For example, during the assembly of devices to which optical fibres are attached, the fibre is positioned to optimise a signal, using a feedback process, before being fixed in place. This positioning will often require multi-axis movement, but with only a small range of travel, as the components of the devices being assembled, and the jigs to hold them, are made accurately. The precision of movements for the positioning process must be of a very high order: movements could need to resolve nanometres of linear travel and arc seconds of angular travel.
With the advent of six axis electronic control, a motorised six axis device can cope with cross-talk between axes, but not with unpredictable motions due to friction, backlash and contaminated lubricants. Also, some six axis devices require all the axes to be power driven to achieve any movements, and this imposes a limitation.
An object of the present invention is to overcome the limitations of prior six axis control mechanisms.
Accordingly, the present invention provides apparatus for the precise positioning of an object relative to a base, comprising, for each of three orthogonal axes, a flexure coupling between the object and the base, at least one of the flexure couplings having a rotary bearing and rotary positioning device where it connects with the object or the base.
The invention also provides a method of positioning a workpiece precisely in three dimensions by coupling it to a base using three orthogonal flexure couplings and rotating at least one of them.
The invention allows six axis positioning, but may be used with fewer axes of rotary control and/or fewer axes of linear control.
We have discovered that flexure mechanisms have significant advantages in this context over conventional mechanics incorporating rolling or sliding bearings. Embodiments of the invention may be operated manually or may be power driven by any axis, or axes may be left without adjustment means. This gives greater flexibility than has been provided by some power driven six axis devices in the past.
Flexure type shaft couplings are of course well known in other technical fields, for coupling a driving and a driven shaft together, for example a motor and a machine spindle. The purpose of the coupling is to allow for angular or linear misalignment and for variations in the separation of the shafts, yet to provide a torsionally stiff connection. Forces resulting from the misalignment have to be kept low to avoid additional shaft bearing loads. This high torsional stiffness and low flexural stiffness in bending and extension of a flexure coupling is used, in the present invention, to produce a simple means of supporting and positioning an object that can be adjusted in up to six axes. Of the two types of flexure shaft couplings in common use, the bellows type is to be preferred over the helical beam type for this application, as the range of movement is much greater, but any type of flexure shaft coupling could be used.
In the context of this invention, the term xe2x80x9cshaft couplingxe2x80x9d refers essentially to the flexure part of the coupling, and the ends fitted to the flexure section for attachment to shafts may or may not be required.
A single bellows, or equivalent, coupling can be replaced by two or more units, with their axes parallel. This arrangement is an alternative to the use of single large diameter couplings where space is limited.